80% of ICPs nodes are held by just 8 separate node provider entities

Because the current boundary nodes are Dfinity controlled and, as implemented now, they cannot be run in a trustless manner. Dfinity engineering team is building a redesigned boundary server model so that independent node providers can apply to run new API Boundary Nodes which are secured from interference in a similar manner to the IC Replica Nodes.
ETA is later this year IIUC, then decentralised boundary node services will become a reality.

See this whole thread for more information: